I know this works because I have done it.
Back in 95 I trained with a high school friend for a year following this theory. My friend went through a week training course with Mike Mentzerand learned "Mike's" way of training. We took it beyond failure but only spent 20 mins. a day, three days a week in the gym!! I gained more muscle in that year than ever before. Then my friend competed in and won a national "get fit" challenge, got a big head, moved off and that was the end of that!
Re: Train less....Gain more....
No need to convert me I was my biggiest and most vascular when my training was short and intense.Shortest was 20 minutes and longest my legs 40 minutes. I was in and outta gym and people did not believe that it was all I was doing But I did not muck around-no talking-pretty much full on all the way
My friend who is getting ready for Worl Amateur Champs is training for two hours with weights I trained with her once and nearly died..not sure how she does it day after day(that does not include cardio time )